Drain pump driving apparatus and laundry treatment machine including the same

ABSTRACT

Disclosed herein is a drain pump driving apparatus and a laundry treatment machine including the same. The drain pump driving apparatus and the laundry treatment machine including the same according to an embodiment of the present invention include a motor to operate the drain pump, an inverter to convert a direct current (DC) power to an alternating current (AC) power by a switching operation and output the converted AC power to the motor, an output current detector to detect an output current flowing to the motor, and a controller to control the inverter, wherein the controller may calculate a speed ripple of the motor based on the output current and performs a control operation based on the calculated speed ripple of the motor to change a speed of the motor.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation Application of U.S. patentapplication Ser. No. 15/490,475 filed Apr. 18, 2017, which claimspriority under 35 U.S.C. § 119 to Korean Patent Application No.10-2016-0047128, filed on 18 Apr. 2016, the disclosures of which areincorporated herein by reference.

BACKGROUND 1. Field

The present invention relates to a drain pump driving apparatus and alaundry treatment machine including the same, and more particularly, toa drain pump driving apparatus capable of reducing noise during drainageand a laundry treatment machine including the same.

2. Background

Generally, a laundry treatment machine performs washing by usingfriction force between laundry and a washing tub that is rotated by adriving force of a motor transmitted thereto with a detergent, washwater and laundry put in a drum. The laundry treatment machine canproduce a laundry washing effect with little damage to the laundry andno tangled laundry.

A drain pump is used to drain residual water from the washing tub in thelaundry treatment machine, and various methods for stable operation ofthe drain pump are being discussed.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the aboveproblems, and it is an object of the present invention to provide adrain pump driving apparatus capable of reducing noise during drainageand a laundry treatment machine including the same.

In accordance with an aspect of the present invention, the above andother objects can be accomplished by the provision of a drain pumpdriving apparatus including a motor to operate the drain pump, aninverter to convert a direct current (DC) power to an alternatingcurrent (AC) power by a switching operation and output the converted ACpower to the motor, an output current detector to detect an outputcurrent flowing to the motor, and a controller to control the inverter,wherein the controller may calculate a speed ripple of the motor basedon the output current and performs a control operation based on thecalculated speed ripple of the motor to change a speed of the motor.

In accordance with another aspect of the present invention, there isprovided a laundry treatment machine including a washing tub, a drivingunit to drive the washing tub, a drain pump, and a drain pump drivingapparatus to drive the drain pump, wherein the drain pump drivingapparatus includes a motor to operate the drain pump, an inverter toconvert a direct current (DC) power to an alternating current (AC) powerby a switching operation and output the converted AC power to the motor,an output current detector to detect an output current flowing to themotor, and a controller to control the inverter, wherein the controllermay calculate a speed ripple of the motor based on the output current,and performs a control operation based on the calculated speed ripple ofthe motor to change a speed of the motor.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments will be described in detail with reference to thefollowing drawings in which like reference numerals refer to likeelements wherein:

FIG. 1 is a perspective view illustrating a laundry treatment machineaccording to an embodiment of the present invention;

FIG. 2 is a side cross-sectional view illustrating the laundry treatmentmachine of FIG. 1;

FIG. 3 is an internal block diagram of the laundry treatment machine ofFIG. 1;

FIG. 4 is an exemplary internal block diagram of the drain pump drivingapparatus of FIG. 1;

FIG. 5 is an exemplary internal circuit diagram of the drain pumpdriving apparatus of FIG. 4;

FIG. 6 is an internal block diagram of the inverter controller of FIG.5;

FIGS. 7A to 7B are views showing various examples of a drain pipeconnected to the drain pump of the laundry treatment machine of FIG. 1;

FIG. 8 is a flowchart showing an exemplary operation method for a drainpump driving apparatus according to an embodiment of the presentinvention, and FIGS. 9A to 10 illustrate the operation method of FIG. 8;

FIG. 11 is a flowchart showing another operation method of a drain pumpdriving apparatus according to an embodiment of the present invention;

FIGS. 12A to 14B illustrate the operation method of FIG. 11;

FIG. 15 is a flowchart illustrating an operation method for a laundrytreatment machine according to an embodiment of the present invention;and

FIGS. 16 to 18C illustrate the operation method of FIG. 15.

DETAILED DESCRIPTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

As used herein, the suffixes “module” and “unit” are added or usedinterchangeably to facilitate preparation of this specification and arenot intended to suggest distinct meanings or functions. Accordingly, theterms “module” and “unit” may be used interchangeably.

FIG. 1 is a perspective view illustrating a laundry treatment machineaccording to an embodiment of the present invention, and FIG. 2 is aside cross-sectional view illustrating the laundry treatment machine ofFIG. 1.

Referring to FIGS. 1 and 2, the laundry treatment machine 100 accordingto an embodiment of the present invention conceptually includes awashing machine having fabric inserted therein for performing washing,rinsing and dewatering, or a dryer having wet fabric inserted therein.The washing machine will be mainly described below.

The washing machine 100 includes a casing 110 forming an outerappearance, operation keys for receiving various control commands from auser, and a control panel 115 equipped with a display for displayinginformation on the operating state of the washing machine 100 to providea user interface, and a door 113 rotatably installed in the casing 110to open and close an entrance hole through which the laundry enters andexits.

The casing 110 includes a body 111 for defining a space in which variouscomponents of the washing machine 100 can be accommodated and a topcover 112 provided at an upper side of the body 111 and forming a fabricentrance hole to allow the laundry to be introduced into an inner tub122 therethrough.

The casing 110 is described as including the body 111 and the top cover112, but the casing 110 is not limited thereto as long as it forms theappearance of the washing machine 100.

A support rod 135 is coupled to the top cover 112 which is one of theconstituent elements of the casing 110. However, the support rod 135 isnot limited thereto and may be coupled to any part of the fixed portionof the casing 110.

The control panel 115 includes operation keys 117 for controlling anoperation state of the laundry treatment machine 100 and a display 118(not shown) disposed on one side of the operation keys 117 to displaythe operation state of the laundry treatment machine 100.

The door 113 opens and closes a fabric entrance hole (not shown) formedin the top cover 112 and may include a transparent member such asreinforced glass to allow the inside of the body 111 to be seen.

The washing machine 100 may include a washing tub 120. The washing tub120 may include an outer tub 124 containing wash water and an inner tub122 rotatably installed in the outer tub 124 to accommodate laundry. Abalancer 134 may be provided at the upper portion of the washing tub 120to compensate for unbalance amount generated when the washing tub 120rotates.

Meanwhile, the washing machine 100 may include a pulsator 133 rotatablyprovided at a lower portion of the washing tub 120.

The driving apparatus 138 serves to provide a driving force for rotatingthe inner tub 122 and/or the pulsator 133. A clutch (not shown) forselectively transmitting the driving force of the driving apparatus 138may be provided such that only the inner tub 122 is rotated, only thepulsator 133 is rotated, or the inner tub 122 and the pulsator 133 arerotated at the same time.

The driving apparatus 138 is operated by a driving unit 220 of FIG. 3,that is, a driving circuit. This will be described later with referenceto FIG. 3 and other drawings.

A detergent box 114 for accommodating various additives such as alaundry detergent, a fabric softener, and/or a bleaching agent isretrievably provided to the top cover 112, and the wash water suppliedthrough a water supply channel 123 flows into the inner tub 122 via thedetergent box.

A plurality of holes (not shown) is formed in the inner tub 122.Thereby, the wash water supplied to the inner tub 122 flows to the outertub 124 through the plurality of holes. A water supply valve 125 forregulating the water supply channel 123 may be provided.

The wash water is drained from the outer tub 124 through a drain channel143. A drain valve 145 for regulating the drain channel 143 and a drainpump 141 for pumping the wash water may be provided.

The support rod 135 is provided to hang the outer tub 124 in the casing110. One end of the support rod 135 is connected to the casing 110 andthe other end of the support rod 135 is connected to the outer tub 124by a suspension 150.

The suspension 150 attenuates vibration of the outer tub 124 during theoperation of the washing machine 100. For example, the outer tub 124 maybe vibrated by vibration generated as the inner tub 122 rotates. Whilethe inner tub 122 rotates, the vibration caused by various factors suchas unbalance laundry amount contained in the inner tub 122, therotational speed of the inner tub 122 or the resonance characteristicsof the inner tub 122 can be attenuated.

FIG. 3 is an internal block diagram of the laundry treatment machine ofFIG. 1.

Referring to FIG. 3, in the laundry treatment machine 100, the drivingunit 220 is controlled by the controller 210, and the driving unit 220drives the motor 230. Thereby, the washing tub 120 is rotated by themotor 230.

The laundry treatment machine 100 may include a motor 630 for drivingthe drain pump 141 and a drain pump driving unit 620 for controlling themotor 630. The drain pump driving unit 620 can be controlled by thecontroller 210.

In this specification, the drain pump driving unit 620 may be referredto as a drain pump driving apparatus 620.

The controller 210 operates according to an operation signal receivedfrom an operation key 117. Thereby, washing, rinsing, and dewatering maybe performed.

In addition, the controller 210 may control the display 118 to display awash course, a wash time, a dewatering time, a rinsing time, or acurrent operation state.

Meanwhile, the controller 210 controls the driving unit 220 to operatethe motor 230. For example, based on a current detector 225 fordetecting the output current flowing through the motor 230 and aposition sensor 235 for sensing the position of the motor 230, thecontroller 210 may control the driving unit 220 to rotate the motor 230.While the detected current and the sensed position signal areillustrated in FIG. 3 as being input to the driving unit 220,embodiments of the present invention are not limited thereto. Thedetected current and the sensed position signal may be applied to eitherthe controller 210 or the controller 210 and the driving unit 220.

The driving unit 220, which serves to drive the motor 230, may includean inverter (not shown) and an inverter controller (not shown). Further,the driving unit 220 may further include a converter or the like forsupplying DC power input to the inverter (not shown).

For example, when the inverter controller (not shown) outputs aswitching control signal (Sic in FIG. 5) of a pulse width modulation(PWM) scheme to the inverter (not shown), the inverter (not shown) maysupply AC power of a predetermined frequency to the motor 230 throughhigh-speed switching.

The controller 210 may calculate the laundry amount based on the currentio detected by the current detector 225 or the position signal H sensedby the position sensor 235. For example, while the washing tub 120rotates, the laundry amount may be calculated based on the current valueio of the motor 230.

The controller 210 may calculate the unbalance amount of the washing tub120, that is, the unbalance (UB) of the washing tub 120. Such unbalanceamount calculation may be performed based on the ripple component of thecurrent io detected by the current detector 225 or the amount of changein rotational speed of the washing tub 120.

FIG. 4 is an exemplary internal block diagram of the drain pump drivingapparatus of FIG. 1, and FIG. 5 is an exemplary internal circuit diagramof the drain pump driving apparatus of FIG. 4.

Referring to FIGS. 4 and 5, the drain pump driving apparatus 620according to an embodiment serves to drive the motor 630 in a sensorlessmanner and includes an inverter 420 and an inverter controller 430.

According to an embodiment, the drain pump driving apparatus 620 mayinclude a converter 410, a DC terminal voltage detector B, a smoothingcapacitor C, and an output current detector E. The drain pump drivingapparatus 620 may further include an input current detector A and areactor L.

Hereinafter, the operation of each constituent unit in the drain pumpdriving apparatus 620 of FIGS. 4 and 5 will be described.

The reactor L is disposed between a commercial AC power source 405 andthe converter 410, and performs a power factor correction operation or aboost operation. The reactor L may also function to limit the harmoniccurrent resulting from high-speed switching of the converter 410.

The input current detector A may detect an input current is input fromthe commercial AC power source 405. To this end, a current transformer(CT), a shunt resistor, or the like may be used as the input currentdetector A. The detected input current is may be input to the invertercontroller 430 as a discrete signal in the form of a pulse.

The converter 410 converts the commercial AC power 405 having passedthrough the reactor L into DC power and outputs the DC power. Althoughthe commercial AC power source 405 is shown as a single-phase AC powersource in FIG. 5, it may be a 3-phase AC power source. The internalstructure of the converter 410 depends on the type of the commercial ACpower source 405.

Meanwhile, the converter 410 may be configured with diodes or the likewithout a switching device, and may perform a rectification operationwithout a separate switching operation.

For example, in the case of a single-phase AC power source, four diodesmay be used in the form of a bridge. In the case of a 3-phase AC powersource, six diodes may be used in the form of a bridge.

As the converter 410, a half-bridge type converter having two switchingdevices and four diodes connected to each other may be used. In the caseof a 3-phase AC power source, six switching devices and six diodes maybe used for the converter.

When the converter 410 is provided with a switching device, the boostoperation, the power factor correction, and the DC power conversion maybe performed by the switching operation of the switching device.

The smoothing capacitor C smooths the input power and stores the same.In FIG. 5, one element is exemplified as the smoothing capacitor C, buta plurality of elements may be provided to secure element stability.

While the smoothing capacitor C is illustrated in FIG. 5 as beingconnected to the output terminal of the converter 410, embodiments ofthe present invention are not limited thereto. The DC power may be inputdirectly to the smoothing capacitor C. For example, the DC power from asolar cell may be input directly to the smoothing capacitor C or may beDC-to-DC converted and input to the smoothing capacitor C. Hereinafter,the parts illustrated in the drawings will be mainly described.

Both ends of the smoothing capacitor C are referred to as DC terminalsor DC links because the DC power is stored.

The DC terminal voltage detector B may detect the DC terminal voltageVdc between both ends of the smoothing capacitor C. To this end, the DCterminal voltage detector B may include a resistance element and anamplifier. The detected DC terminal voltage Vdc may be input to theinverter controller 430 as a discrete signal in the form of a pulse.

The inverter 420 may include a plurality of inverter switching devices.The inverter 420 may convert the smoothed DC power Vdc into 3-phase ACpowers va, vb and vc having predetermined frequencies by the on/offoperation of the switching device, and output the same to a 3-phasesynchronous motor 630.

The inverter 420 includes upper switching devices Sa, Sb and Sc andlower switching devices S′a, S′b and S′c. Each of the upper switchingdevices Sa, Sb, Sc and a corresponding lower switching device S′a, S′b,S′c are connected in series to form a pair. Three pairs of upper andlower switching devices Sa and S′a, Sb and S′b, and Sc and S′c areconnected in parallel. Each of the switching devices Sa, S′a, Sb, S′b,Sc and S′c is connected with a diode in anti-parallel.

Each of the switching devices in the inverter 420 is turned on/off basedon an inverter switching control signal Sic from the inverter controller430. Thereby, 3-phase AC power having a predetermined frequency isoutput to the 3-phase synchronous motor 630.

The inverter controller 430 may control the switching operation of theinverter 420 in a sensorless manner. To this end, the invertercontroller 430 may receive an output current idc detected by the outputcurrent detector E.

In order to control the switching operation of the inverter 420, theinverter controller 430 outputs the inverter switching control signalSic to the inverter 420. The inverter switching control signal Sic is apulse width modulated (PWM) switching control signal. The inverterswitching control signal Sic is generated and output based on the outputcurrent idc detected by the output current detector E. The operation ofoutputting the inverter switching control signal Sic from the invertercontroller 430 will be described in detail with reference to FIG. 6later in this specification.

The output current detector E may detect the output current idc flowingbetween the inverter and the 3-phase motor 630.

The output current detector E may be disposed between the DC linkcapacitor C and the inverter 420 to detect an output current flowing tothe motor.

In particular, the output current detector E may include one shuntresistance element Rs.

The output current detector E may use one shunt resistor element Rs todetect a phase current which is the output current idc flowing to themotor 630 in time division manner when the lower switching devices ofthe inverter 420 are turned on.

The detected output current idc, which is a discrete signal in the formof a pulse, may be applied to the inverter controller 430, and theinverter switching control signal Sic is generated based on the detectedoutput current idc. Hereinafter, it is assumed that the detected outputcurrent idc includes 3-phase output currents ia, ib and ic.

The 3-phase motor 630 includes a stator and a rotor. The rotor rotateswhen the AC power of each phase of a predetermined frequency is appliedto the coil of a corresponding phase (of phases a, b and c) of thestator.

Such motor 630 may include a brushless DC (BLDC) motor.

The motor 630 may include, for example, a Surface-MountedPermanent-Magnet Synchronous Motor (SMPMSM), an Interior PermanentMagnet Synchronous Motor (IPMSM), and a Synchronous Reluctance Motor(SynRM). The SMPMSM and the IPMSM are Permanent Magnet SynchronousMotors (PMSM) employing permanent magnets, while the SynRM does not havea permanent magnet.

FIG. 6 is an internal block diagram of the inverter controller of FIG.5.

Referring to FIG. 6, the inverter controller 430 may include an axistransformation unit 510, a speed calculator 520, a power calculator 321,a speed command generator 323, a current command generator 530, avoltage command generator 540, an axis transformation unit 550, and aswitching control signal output unit 560.

The axis transformation unit 510 may extract the respective phasecurrents ia, ib and ic from the output current idc detected by theoutput current detector E and transform the extracted phase currents ia,ib and ic, into 2-phase currents (iα, iβ) in the stationary coordinatesystem.

The axis transformation unit 510 may transform the 2-phase currents (iα,iβ) of the stationary coordinate system into 2-phase current (id, iq) ofthe rotating coordinate system.

The speed calculator 520 may estimate the position {circumflex over(θ)}_(r) based on the output current idc detected by the output currentdetector E and calculate the speed {circumflex over (ω)}_(r) bydifferentiating the estimated position.

The power calculator 321 may calculate the power or load of the motor630 based on the output current idc detected by the output currentdetector E.

The speed command generator 323 generates a speed command value ω*_(r)based on the power P calculated by the power calculator 321 and a powercommand value P*_(r). For example, the speed command generator 323 mayperform PI control in the PI controller 325 based on the differencebetween the calculated power P and the power command value P*_(r), andgenerate a speed command value ω*_(r).

The current command generator 530 generates a current command valuei*_(q) based on the calculated speed {circumflex over (ω)}_(r) and aspeed command value ω*_(r). For example, the current command generator530 may perform PI control in a PI controller 535 and generate thecurrent command value i*_(q) based on the difference between thecalculated speed {circumflex over (ω)}_(r) and the speed command valueω*_(r). While FIG. 6 illustrates a q-axis current command value i*_(q)as a current command value, a d-axis current command value i*_(d) mayalso be generated. The d-axis current command value i*_(d) may be set to0.

The current command generator 530 may further include a limiter (notshown) for limiting the level of the current command value i*_(q) suchthat the current command value i*_(q) does not exceed an allowablerange.

Next, the voltage command generator 540 generates d-axis and q-axisvoltage command values v*_(d) and v*_(q) based on the d-axis and q-axiscurrents i_(d) and i_(q) which are transformed into currents in the2-phase rotating coordinate system by the axis transformation unit andthe current command values i*_(d) and i*_(q) from the current commandgenerator 530. For example, the voltage command generator 540 mayperform PI control in a PI controller 544 and generate a q-axis voltagecommand value v*_(q) based on the difference between the q-axis currenti_(q) and the q-axis current command value i*_(q). In addition, thevoltage command generator 540 may perform PI control in a PI controller548 and generate the d-axis voltage command value v*_(d) based on thedifference between the d-axis current i_(d) and the d-axis currentcommand value i*_(d). The voltage command generator 540 may furtherinclude a limiter (not shown) for limiting the levels of the d-axis andq-axis voltage command values v*_(d) and v*_(q) such that the d-axis andq-axis voltage command values v*_(d) and v*_(q) do not exceed anallowable range.

The generated d-axis and q-axis voltage command values v*_(d) and v*_(q)are input to the axis transformation unit 550.

The axis transformation unit 550 receives the position {circumflex over(θ)}_(r) calculated by the speed calculator 520 and the d-axis andq-axis voltage command values v*_(d) and v*_(q) and performs coordinatesystem transformation.

The axis transformation unit 550 transforms a 2-phase rotatingcoordinate system into a 2-phase stationary coordinate system. Thetransformation may be performed using the position {circumflex over(θ)}_(r) calculated by the speed calculator 520.

The axis transformation unit 550 may also transform the 2-phasestationary coordinate system into the 3-phase stationary coordinatesystem. Through such transformation, the axis transformation unit 550outputs 3-phase output voltage command values v*a, v*b, and v*c.

The switching control signal output unit 560 outputs a PWM inverterswitching control signal Sic based on the 3-phase output voltage commandvalues v*a, v*b, and v*c.

The output inverter switching control signal Sic is transformed into agate drive signal in a gate driving unit (not shown) and is then inputto the gate of each switching device in the inverter 420. Thereby, theswitching devices Sa, S′a, Sb, S′b, Sc, and S′c in the inverter 420perform the switching operation.

FIGS. 7A to 7B are views showing various examples of a drain pipeconnected to the drain pump of the laundry treatment machine of FIG. 1.

FIG. 7A illustrates a case where the difference in height between thedrain pump 141 and the drain pipe 199 a is ha. FIG. 7B illustrates acase where the difference in height between the drain pump 141 and thedrain pipe 199 a is hb, which is greater than ha.

For example, ha may be approximately 0.9 m and hb may be approximately2.4 m.

If the laundry treatment machine 100 is installed in a basement, thedrain pipe 199 a should extend to the ground for draining, andtherefore, as shown in FIGS. 7A and 7B, it should extend to a positionsubstantially higher than the drain pump 141.

In this case, if the drain pump is implemented using a solenoid,drainage will not be performed smoothly due to the low pumping power.

Accordingly, a motor is preferably used to drive the drain pump.Conventionally, an AC motor has been employed and driven at a constantspeed of approximately 3000 rpm or 3600 rpm using an AC power of 50 Hzor 60 Hz.

In this case, since the motor is driven at a constant speed irrespectiveof the height of the drain pump, noise is generated by movement of theresidual water remaining in the drain pipe 199 a.

It is assumed in the present invention that a motor 630 capable ofvarying the speed is used in order to solve the problem above.

That is, according to an embodiment of the present invention, the motor63 for driving the drain pump 141 may include a brushless DC (BLDC)motor 630. This will be described with reference to FIG. 8.

Further, in the present invention, a lift, which is a difference betweenthe water level of a water introduction part through which water flowsinto the drain pump 141 and the water level of a water discharge partfor discharging water from the drain pump 141 is calculated, and therotational speed of the motor 630 is varied based on the calculatedlift.

According to this configuration, the lift may be accurately calculatedwithout using any water pressure sensor or water level sensor.Therefore, manufacturing costs may be reduced.

As the rotational speed of the motor 630 is controlled to be variedbased on the calculated lift, drainage may be performed smoothly, andpower consumption may be reduced. Details will be described withreference to FIG. 11 and subsequent figures.

FIG. 8 is a flowchart showing an exemplary operation method for a drainpump driving apparatus according to an embodiment of the presentinvention, and FIGS. 9A to 10 illustrate the operation method of FIG. 8.

Referring to FIG. 8, the inverter controller 430 of the drain pumpdriving apparatus or the controller 210 of the laundry treatment machinecontrols the motor 630 to rotate at a first speed (S710).

Next, the output current detector E of the drain pump driving unit 620detects the output current Idc flowing to the motor 630 (S720).

Next, the inverter controller 430 of the drain pump driving apparatus orthe controller 210 of the laundry treatment machine calculates the speedand speed ripple of the motor 630 based on the detected output currentIdc (S730).

The inverter controller 430 of the drain pump driving apparatus maycalculate the motor speed based on the detected output current Idc asdescribed with reference to FIG. 6.

The inverter controller 430 of the drain pump driving apparatus maycalculate a ripple that indicates a change in the calculated speed.

Next, the inverter controller 430 of the drain pump driving apparatus orthe controller 210 of the laundry treatment machine performs a controloperation based on the calculated motor speed ripple to change the motorspeed (S740).

The inverter controller 430 of the drain pump driving apparatus or thecontroller 210 of the laundry processing device may control the speed ofthe motor to be decreased sequentially or stepwise as the calculatedmotor speed ripple increases.

Accordingly, the noise generated by the residual water may be reducedwhen the laundry treatment machine 100 is drained.

Particularly, when the laundry treatment machine 100 performs thedewatering process without the washing process and the rinsing process,the inverter controller 430 of the drain pump driving apparatus or thecontroller 210 of the laundry treatment machine may calculate the speedripple of the motor based on the output current Idc, and perform acontrol operation based on the calculated motor speed ripple to changethe speed of the motor. Thereby, noise caused by residual waterremaining in the drain pipe and the BLDC may be reduced.

FIG. 9A illustrates rotating the motor 630 at a speed of ωk.

When the motor rotates at the speed of ωk, the inverter controller 430of the drain pump driving apparatus or the controller 210 of the laundrytreatment machine may calculate the speed and speed ripple on the basisof the output current Idc detected by the output current detector E.

For example, a speed ripple corresponding to the speed ripple waveformshown in FIG. 9C may be calculated.

This speed ripple may be caused by residual water 198 a and 198 b movingin the drain pipe 199 a as shown in FIG. 9B.

For example, when the motor 630 of the drain pump 141 is operated at thespeed of ωk, the residual water 198 a and 198 b may reciprocate betweenthe drain pump 141 and the drain pipe 199 a.

Particularly, when the water moves toward the drain pump 141, themovement affects the motor 630 rotating at the speed of ωk, and thusripples are generated in the motor 630. Thereby, noise is generated.

The inverter controller 430 of the drain pump driving apparatus or thecontroller 210 of the laundry treatment machine may perform a controloperation based on the speed ripple ωri of FIG. 9C to change the speedof the motor so as to reduce noise.

The inverter controller 430 of the drain pump driving apparatus or thecontroller 210 of the laundry treatment machine may control the speed ofthe motor to sequentially decrease as shown in FIG. 9D as the calculatedmotor speed ripple increases.

The inverter controller 430 of the drain pump driving apparatus or thecontroller 210 of the laundry treatment machine may control the speed ofthe motor to decrease stepwise as shown in FIG. 9E as the calculatedmotor speed ripple increases.

FIG. 10(a) illustrates an output current waveform Idc1 and a motor speedwaveform Vcd1 obtained when the driving method of FIG. 8 is not used,and FIG. 10(b) illustrates an output current waveform Idc2 and a motorspeed waveform Vcd2 obtained when the driving method of FIG. 8 is used.

Referring to FIG. 10, it can be seen that, when the driving method ofFIG. 8 is not used, a significant ripple component occurs in the motorspeed waveform Vcd1 during the period Pm3. As a result, significantnoise is generated.

On the other hand, when the driving method of FIG. 8 is used, the ripplecomponent is significantly reduced in the motor speed waveform Vcd2during all periods including the period Pm3. Thereby, noise may besignificantly reduced, and the motor 630 of the drain pump 141 may bestably driven.

FIG. 11 is a flowchart showing another operation method of a drain pumpdriving apparatus according to an embodiment of the present invention,and FIGS. 12A to 14B illustrate the operation method of FIG. 11.

Referring to FIG. 11, the inverter controller 430 of the drain pumpdriving apparatus or the controller 210 of the laundry treatment machinecontrols the motor 630 to rotate at a first speed (S810).

Next, the output current detector E of the drain pump driving unit 620detects the output current Idc flowing through the motor 630 (S820).

Next, the inverter controller 430 of the drain pump driving apparatus orthe controller 210 of the laundry treatment machine calculates the speedof the motor 630 based on the detected output current Idc (S830).

The inverter controller 430 of the drain pump driving apparatus maycalculate the motor speed based on the detected output current Idc asdescribed with reference to FIG. 6.

Next, the inverter controller 430 of the drain pump driving apparatus orthe controller 210 of the laundry treatment machine calculates a liftbased on the calculated motor speed (S840).

The inverter controller 430 of the drain pump driving apparatus or thecontroller 210 of the laundry treatment machine may calculate the lift,which is a difference between the water level of a water introductionpart through which water flows into the drain pump 141 and the waterlevel of a water discharge part for discharging water from the drainpump 141.

For example, the inverter controller 430 of the drain pump drivingapparatus or the controller 210 of the laundry treatment machine maycalculate the difference between the bottom surface of the washing tub120 and the final height of the drain pipe 199 a as the lift.

As another example, the inverter controller 430 of the drain pumpdriving apparatus or the controller 210 of the laundry treatment machinemay calculate the difference between the position of the drain pump 141,which is lower than the bottom surface of the washing tub 120, and thefinal position of the drain pipe 199 a as the lift.

The inverter controller 430 of the drain pump driving apparatus or thecontroller 210 of the laundry treatment machine may control the motor630 to rotate at a first speed. When rotation at the first speed iscontrolled, if the speed of the motor 630 calculated based on the outputcurrent Idc is a second speed, the lift may be calculated as a firstlevel based on the second speed.

The inverter controller 430 of the drain pump driving apparatus or thecontroller 210 of the laundry treatment machine may control the motor630 to rotate at a first speed. When rotation at the first speed iscontrolled, if the speed of the motor 630 calculated based on the outputcurrent Idc is a third speed lower than the second speed, the lift maybe calculated as a second level higher than the first level.

The inverter controller 430 of the drain pump driving apparatus or thecontroller 210 of the laundry treatment machine may calculate a lowerlevel of the lift as the calculated speed of the motor 630 is lowered.

Next, the inverter controller 430 of the drain pump driving apparatus orthe controller 210 of the laundry treatment machine varies the motorspeed based on the calculated lift (S850).

The inverter controller 430 of the drain pump driving apparatus or thecontroller 210 of the laundry treatment machine may control therotational speed of the motor 630 to be varied based on the calculatedlift such that the speed of the motor 630 decreases as the water levelof the water introduction part is lowered.

FIG. 12A depicts a case where the motor 630 rotates at a speed of ω1during the period Pa, and gradually slows down during the period Pb,which is a transition period, and then rotates at a speed of ω2 lowerthan ω1 during the period Pc.

The inverter controller 430 of the drain pump driving apparatus or thecontroller 210 of the laundry treatment machine controls the motor 630to rotate at the actual speed command value ω1. If the speed of themotor 630 calculated based on the output current is ω2, the lift may becalculated based on the difference between ω1 and ω2.

For example, as shown in FIG. 12B, the lift, which is the differencebetween the position of the drain pump 141 and the final height of thedrain pipe 199 a, may be calculated as hb.

The data on the lift for the speed difference may be a value preset byan experiment, and may be pre-stored in a lookup table or memory.

FIG. 12A depicts a case where the motor 630 rotates at a speed of ω1during the period Pa, and gradually slows down during the period Pb,which is a transition period, and then rotates at a speed of ω3 lowerthan ω1 during the period Pc.

The inverter controller 430 of the drain pump driving apparatus or thecontroller 210 of the laundry treatment machine controls the motor 630to rotate at the actual speed command value ω1. If the speed of themotor 630 calculated based on the output current is ω3, the lift may becalculated based on the difference between ω1 and ω3.

Here, ω3 may be less than ω2.

Accordingly, as shown in FIG. 12D, the lift, which is the differencebetween the position of the drain pump 141 and the final height of thedrain pipe 199 a, may be calculated as ha.

That is, the inverter controller 430 of the drain pump driving apparatusor the controller 210 of the laundry treatment machine may calculate alower level of the lift as the calculated speed of the motor 630 islowered.

Since the level of the lift can be calculated on the basis of the speedof the motor 630 calculated based on the output current as describedabove, the lift may be accurately calculated without using any separatewater pressure sensor or water level sensor.

FIG. 13A illustrates that the water level in the washing tub 120 issequentially lowered.

In particular, FIG. 13A corresponds to FIG. 7B in terms of the positionof the drain pipe 199 a.

FIG. 13A(a) illustrates a case where the difference between the waterlevel of the washing tub and the height of the drain pipe 199 a is hb1,FIG. 13A(b) illustrates a case where the difference between the waterlevel of the washing tub and the height of the drain pipe 199 a is hb2,and FIG. 13A(c) illustrates a case where the water level of the washingtub is zero.

The inverter controller 430 of the drain pump driving apparatus or thecontroller 210 of the laundry treatment machine may control therotational speed of the motor 630 to be varied based on the calculatedlift such that the speed of the motor 630 decreases as the water levelof the water introduction part is lowered, as described above.

FIG. 13B illustrates decrease in the driving speed of the motor 630 fromωaa to ωab to ωac when the water level of the washing tub issequentially lowered as shown in FIG. 13A.

The driving speed ωaa may correspond to hb1 which is the differencebetween the water level of the washing tub and the drain pipe 199 a inFIG. 13A(a), ωab may correspond to hb2 which is the difference betweenthe water level of the washing tub and the drain pipe 199 a in FIG.13A(b), and wac may correspond to hb in FIG. 13A(c).

FIG. 14A illustrates sequential lowering of the water level in thewashing tub 120.

In particular, FIG. 14A corresponds to FIG. 7A in terms of the positionof the drain pipe 199 a.

FIG. 14A(a) illustrates a case where the difference between the waterlevel of the washing tub and the height of the drain pipe 199 a is hb1,FIG. 14A(b) illustrates a case where the difference between the waterlevel of the washing tub and the height of the drain pipe 199 a is hb2,and FIG. 14A(c) illustrates a case where the water level of the washingtub is zero.

The inverter controller 430 of the drain pump driving apparatus or thecontroller 210 of the laundry treatment machine may control therotational speed of the motor 630 to be varied based on the calculatedlift such that the speed of the motor 630 decreases as the water levelof the water introduction part is lowered, as described above.

FIG. 14B illustrates decrease in the driving speed of the motor 630 fromωba to ωbb to ωbc when the water level of the washing tub issequentially lowered as shown in FIG. 14A.

The driving speed ωba may correspond to ha1, which is the differencebetween the water level of the washing tub and the drain pipe 199 a inFIG. 14A(a), ωbb may correspond to ha2, which is the difference betweenthe water level of the washing tub and the drain pipe 199 a in FIG.14A(b), and ωbc may correspond to ha in FIG. 14A(c).

The value of ωba may be less than ωaa of FIG. 13B. That is, as the levelof the lift is lowered, the speed of the motor 630 may decrease.

FIGS. 11 and 12 illustrate a lift calculation method based on the outputcurrent. Similarly, it is also possible to calculate the lift based onthe power calculated in the power calculator of FIG. 6.

The inverter controller 430 of the drain pump driving apparatus or thecontroller 210 of the laundry treatment machine may calculate a lowerlevel of the lift as the calculated power or load is lowered.

FIG. 15 is a flowchart illustrating an operation method for a laundrytreatment machine according to an embodiment of the present invention,and FIGS. 17 to 18C illustrate the operation method of FIG. 15.

Referring to FIG. 15, the controller 210 of the laundry treatmentmachine primarily calculates the laundry amount in the washing tub(S1505).

Various methods may be used to calculate the laundry amount.

For example, as a method of sensing the laundry amount according to anembodiment of the present invention, the laundry amount in the washingtub may be calculated based on based on a current command value fordriving the motor during an acceleration period and a current commandvalue for driving the motor during a constant speed period. Further, thecounter electromotive force generated from the motor during the constantspeed period may be calculated, and the calculated counter electromotiveforce may be reflected in sensing the amount laundry. Thereby,calculating of the laundry amount may be more accurate.

As another example of sensing the laundry amount, rotation of thewashing tub may be accelerated, and the laundry amount in the washingtub may be calculated based on a current command value for driving themotor for rotating the washing tub during the acceleration period or anoutput current flowing to the motor.

Next, the controller 210 determines whether the calculated laundryamount is greater than or equal to a reference value (S1510). If thecalculated laundry amount is less than the reference value, thecontroller performs step S1565, determining that the laundry is dry. Ifthe calculated laundry amount is greater than or equal to the referencevalue, the controller performs step S1515 and subsequent steps.

The controller 210 determines that the laundry is dry if the calculatedlaundry amount is less than the reference value. If the calculatedlaundry amount is greater than or equal to the reference value, thecontroller 210 performs step S1515 and subsequent steps in considerationof a possibility that the laundry is wet.

Next, the controller 210 controls water to be supplied to in the washingtub up to a first water level (S1515). Then, the controller 210 controlsthe motor for rotating the washing tub to rotate in the normal andreverse directions (S1520). Then, the controller 210 calculates thewater level in the washing tub (S1525).

FIG. 18A illustrates supply of water into the outer tub 124 of thewashing tub up to a first water level. To this end, the controller 210may control the water supply valve 125 for regulating the water supplychannel 123. That is, the controller 210 may control the water supplyvalve 125 so as to supply water up to the first water level.

Next, FIG. 18B illustrates that the motor for rotating the washing tubrotates in the normal and reverse directions. This operation is intendedto completely soak the laundry in the water in the washing tub after thewater is supplied. It is also possible to rotate the motor forward orbackward for a predetermined time.

Next, FIG. 18C illustrates lowering of the water level with the laundrycontaining the supplied water on the basis of forward and reverserotations of the motor of FIG. 18B.

Measurement of the water level may be performed through a water levelsensor. For example, the water level frequency at the zero water levelmay be 28 KHz, H1 may be a water level frequency of 25.9 KHz, and H2 maybe a water level frequency of about 26.5 KHz. The water level frequency,that is, the water level value may be inversely proportional to thewater level in the washing tub.

In an embodiment of the present invention, the water level frequency maybe used to determine dry laundry/wet laundry and to calculate the amountof wet laundry. For details, refer to step S1550.

Next, the controller 210 determines whether the first water level ishigher than the calculated water level (S1530), and if so, controlswater to be resupplied up to the first water level (S1535).

To this end, the controller 210 may control the water supply valve 125for regulating the water supply channel 123. That is, the controller 210may control the water supply valve 125 so as to resupply water up to thefirst water level.

Next, the controller 210 secondarily calculates the laundry amount inthe washing tub (S1540). Next, the controller 210 determines whether thelaundry is dry or wet using the primarily calculated laundry amount, thesecondarily calculated laundry amount, and the calculated water levelvalue (S1550).

As described in step S1505, the secondary sensing of the laundry amountmay be performed using various methods.

The controller 210 determines that the laundry is wet as the primarilycalculated laundry amount increases or the calculated water level valuedecreases.

That is, the controller 210 determines that the laundry is wet as theprimarily calculated laundry amount decreases or the calculated waterlevel value increases.

Alternatively, as the difference between the calculated water levelvalue and the first water level value increases, the controller 210determines that the laundry is wet.

In the case of wet laundry, step S1550 is performed. In the case of drylaundry, step S1565 is performed.

That is, in the case of wet laundry, the controller 210 calculates thewet laundry amount based on the primarily calculated laundry amountvalue, the secondarily calculated laundry amount value, and thecalculated water level value (S1550). Here, the wet laundry amountrefers to an original laundry amount that does not contain moisture.

Calculation of the wet laundry amount may be performed by subtractingthe amount of water from the amount of the water and laundry. That is,this operation may mean calculating the original laundry amount.

Increase in the difference between the secondarily calculated laundryamount value and the primarily calculated laundry amount value means wetlaundry having a smaller amount of water. Decrease in the differencebetween the secondarily calculated laundry amount value and theprimarily calculated laundry amount value means wet laundry having alarger amount of water.

Meanwhile, increase in the water level frequency of the calculated waterlevel means wet laundry having a larger amount of water, and decrease inthe water level frequency of the calculated water level means wetlaundry having a smaller amount of water.

Accordingly, as the difference between the secondarily calculatedlaundry amount value and the primarily calculated laundry amount valueincreases, or the water level frequency of the calculated water leveldecreases, the wet laundry amount may increase. Alternatively, as thedifference between the calculated water level value and the first waterlevel value decreases, the wet laundry amount may increase.

That is, the wet laundry amount may decrease as the difference betweenthe secondarily calculated laundry amount value and the primarilycalculated laundry amount value decreases, or the water level frequencyof the calculated water level increases. Alternatively, the wet laundryamount may decrease as the difference between the calculated water levelvalue and the first water level value increases.

As described above, according to an embodiment of the present invention,laundry can be treated in accordance with its own weight by sensing theoriginal laundry amount that does not contain moisture. Thereby, thewashing time may be shortened, and the amount of water used may bereduced. As a result, the energy consumed in the laundry treatmentmachine may be reduced.

In the case of dry laundry, the controller 210 calculates the drylaundry amount based on the primarily calculated laundry amount value(S1565).

Based on the primarily calculated laundry amount value, the controller210 may determine that the dry laundry amount increases as the primarilycalculated laundry amount value increases.

It is possible to output the dry laundry amount through the table 1200in FIG. 12. A current command value between the acceleration period andthe constant speed period may be divided into a plurality of periodsSe1, . . . , Se10 and the dry laundry amount may be output based on eachcorresponding current command value, that is, a calculated value. Thatis, any one of L1 to L10 may be output as the dry laundry amount.

In order to calculate the laundry amount in the laundry treatmentmachine, the driving unit 220 first aligns the motor 230 that rotatesthe washing tub 120. That is, the driving unit 220 controls the motor230 so as to fix the rotor of the motor 230 at a predetermined position.That is, a predetermined current is applied to the motor 230.

Such a motor alignment period may correspond to the period Ta in FIG.15.

For example, it is possible to apply a current having a predeterminedmagnitude to the motor 230 during the motor alignment period Ta.Thereby, the rotor of the motor 230 is moved to a predeterminedposition.

As another example, it is also possible to apply currents of differentmagnitudes during the motor alignment period Ta. This operation isintended to calculate a motor constant which may be used in calculatingthe counter electromotive force in a constant-speed rotation period Tc,which will be described later. Here, the motor constant may mean, forexample, the equivalent resistance value Rs of the motor 230 or thelike.

FIG. 16 illustrates that, in the motor alignment period Ta, a currentI_(B1) of a first magnitude flows to the motor 230 during a first periodTa1 and a current I_(B2) of a second magnitude flows to the motor 230during the second period Ta2.

Here, the length of the first period Ta1 may be equal to that of thesecond period Ta2, and the second magnitude of the current I_(B2) may betwice the first magnitude of the current I_(B1).

Next, the driving unit 220 accelerates rotation of the motor 230 forrotating the washing tub 120. Specifically, the driving unit 220 mayaccelerate rotation of the motor 230 from the stationary state to afirst speed ω1. To accelerate the rotation, the current command valueapplied to the motor 230 may be sequentially increased.

The first speed ω1 is a speed at which the resonance band of the washingtub 120 can be avoided, and may be between about 40 rpm and 50 rpm.

Such a motor accelerating rotation period may correspond to period Tb inFIG. 15.

Then, the driving unit 220 rotates the motor 230, which serves to rotatethe washing tub 120, at a constant speed. Specifically, after rotationof the motor 230 reaches the first speed ω1 through acceleration, thedriving unit 220 may rotate the motor 230 at a constant speed, which isa second speed ω2. For constant-speed rotation, the current commandvalue applied to the motor 230 may be constant.

The second speed ω2 may be lower than the first speed ω1 and may bebetween about 25 rpm and about 35 rpm.

Such a motor constant-speed rotation period may correspond to period Tcin FIG. 15.

The controller 210 may perform laundry amount sensing based on thedifference between the average value of the current command values forrotating the motor 230 during the acceleration period and the averagevalue of the current command values for rotating the motor 230 duringthe constant-speed period. Thereby, the laundry amount may beefficiently calculated.

The current command value for rotating the motor 230 in the accelerationperiod means a current command value in which the inertia component andthe frictional force component are combined and the current commandvalue for rotating the motor 230 in the constant-speed period may mean acurrent command value corresponding to the frictional force componentwithout the inertia component corresponding to the acceleration.

The laundry amount sensing described in FIGS. 15 to 18C may be performedin each of the washing, rinsing, and dewatering processes.

Then, after the laundry amount is calculated, the introduced water maybe drained. At this time, the drain pump driving apparatus 620 describedin FIGS. 1 to 14 may operate.

That is, the inverter controller 430 of the drain pump driving apparatus620 or the controller 210 of the laundry treatment machine may calculatethe speed ripple of the motor based on the output current Idc, andperform a control operation based on the calculated motor speed rippleto change the speed of the motor. Thereby, noise caused by residualwater remaining in the drain pipe may be reduced.

Meanwhile, the inverter controller 430 of the drain pump drivingapparatus 620 or the controller 210 of the laundry treatment machine maycalculate the speed of the motor based on the output current, andcalculate a lift, which is a difference between the water level of awater introduction part through which water flows into the drain pumpand the water level of a water discharge part for discharging water fromthe drain pump based on the calculated motor speed. Accordingly, thelift may be accurately calculated without using a water pressure sensorand a water level sensor. Therefore, manufacturing costs may be reduced.

While FIG. 1 illustrates a top loading type machine as a laundrytreatment machine, the drain pump driving apparatus 620 according to anembodiment of the present invention may also be applied to afront-loading washing machine, that is, a drum type washing machine.

The drain pump driving apparatus and the laundry treatment machinehaving the same according to embodiments of the present invention arenot limited to the configuration and method of the embodiments describedabove. Variations may be made to the embodiments described above byselectively combining all or some of the embodiments.

A method for operating the drain pump driving apparatus and the laundrytreatment machine of the present invention is implementable by codereadable a processor provided to each of the drain pump drivingapparatus, on a recording medium readable by the processor. Therecording medium readable by the processor includes all kinds ofrecording devices for storing data which can be read by the processor.

As is apparent from the above description, the present invention has thefollowing effects.

A drain pump driving apparatus and a laundry treatment machine includingthe same according to embodiments of the present invention include amotor to operate the drain pump and an inverter for converting DC powerinto AC power through a switching operation and outputting the convertedAC power to the motor, an output current detector to detect an outputcurrent flowing to the motor, and a controller to control the inverter.The controller may calculate speed ripple of the motor based on theoutput current, and vary the speed of the motor based on the calculatedspeed ripple of the motor. As a result, noise produced during drainagemay be reduced.

Particularly, as the calculated speed ripple of the motor becomeslarger, the speed of the motor is controlled so as to be reducedgradually or stepwise. Thereby, noise produced during drainage may bereduced.

The controller may calculate the speed of the motor based on the outputcurrent, and calculate a lift, which is a difference between the waterlevel of a water introduction part through which water flows into thedrain pump and the water level of a water discharge part for dischargingwater from the drain pump based on the calculated motor speed.Accordingly, the lift may be accurately calculated without using a waterpressure sensor and a water level sensor. Therefore, manufacturing costsmay be reduced.

In addition, by controlling the rotational speed of the motor to bevaried based on the calculated lift, drainage may be performed smoothly,and power consumption may be reduced.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

Any reference in this specification to “one embodiment,” “anembodiment,” “example embodiment,” etc., means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of such phrases in various places in the specification arenot necessarily all referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with any embodiment, it is submitted that it is within thepurview of one skilled in the art to affect such feature, structure, orcharacteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

What is claimed is:
 1. A drain pump driving apparatus comprising: amotor to drive a drain pump; an inverter to convert, based on aswitching operation, a direct current (DC) power to an alternatingcurrent (AC) power, and the inverter to provide the converted AC powerto the motor; and a controller to control the inverter, wherein thedrain pump is connected to a drain pipe, and a height of the drain pipeis greater than a height of the drain pump and a height of a bottomsurface of a washing tub, wherein when dewatering process is performed,the controller is configured to change a speed of the motor based onmotor speed ripple generated by movement of residual water remaining inthe drain pipe during the rotating of the motor.
 2. The drain pumpdriving apparatus according to claim 1, wherein the controller isconfigured to control the speed of the motor to decrease sequentially orto decrease stepwise as the motor speed ripple increases.
 3. The drainpump driving apparatus according to claim 1, further comprising anoutput current detector to detect an output current flowing to themotor, wherein the controller is configured to calculate a lift based onthe output current, wherein the lift corresponds to a difference betweena water level of a water introduction part flowing into the drain pumpand a water level of a water discharge part discharged from the drainpump.
 4. The drain pump driving apparatus according to claim 3, whereinthe controller is configured to change a rotational speed of the motorbased on the calculated lift.
 5. The drain pump driving apparatusaccording to claim 3, wherein the controller is configured to rotate themotor at a first speed, wherein, when the speed of the motor, determinedbased on the output current, is a second speed during the rotation ofthe motor at the first speed, the controller is configured to determinethe lift as a first level based on the second speed.
 6. The drain pumpdriving apparatus according to claim 5, wherein the controller isconfigured to rotate the motor at the first speed, wherein, when thespeed of the motor, determined based on the output current, is a thirdspeed during the rotation of the motor at the first speed, thecontroller is configured to determine the lift as a second level, thesecond level to be higher than the first level, and the third speed isto be less than the second speed.
 7. The drain pump driving apparatusaccording to claim 3, wherein the controller is configured to determinea lower level of the lift while the calculated speed of the motor is tobe lowered.
 8. The drain pump driving apparatus according to claim 3,wherein the controller is configured to change a rotational speed of themotor based on the calculated lift such that the speed of the motor isto decrease while the water level of the water introduction part is tobe lowered.
 9. The drain pump driving apparatus according to claim 1,wherein the motor includes a brushless DC motor.
 10. The drain pumpdriving apparatus according to claim 1, further comprising: an outputcurrent detector to detect an output current flowing to the motor; a DClink capacitor to store the DC power, wherein the output currentdetector is disposed between the DC link capacitor and the inverter. 11.The drain pump driving apparatus according to claim 10, wherein thecontroller includes: a power calculator to determine a power or a loadof the motor based on the output current; a speed command generator toprovide a speed command value based on the determined power; a currentcommand generator to provide a current command value based on the speedcommand value and the determined speed of the motor; a voltage commandgenerator to provide a voltage command value based on the currentcommand value and the output current; and a switching control signaloutput device to provide a switching control signal based on the voltagecommand value, the switching control signal for controlling driving ofthe inverter.
 12. The drain pump driving apparatus according to claim11, wherein the controller includes: a speed calculator to determine thespeed of the motor based on the output current.
 13. A laundry treatmentmachine comprising: a washing tub; a driving device to drive the washingtub; a drain pump; and a drain pump driving apparatus to drive the drainpump, wherein the drain pump driving apparatus includes: a motor todrive the drain pump; an inverter to convert a direct current (DC) powerto an alternating current (AC) power by a switching operation, and theinverter to provide the converted AC power to the motor; and acontroller to control the inverter, wherein the drain pump is connectedto a drain pipe, and a height of the drain pipe is greater than a heightof the drain pump and a height of a bottom surface of the washing tub,wherein when dewatering process is performed, the controller isconfigured to change a speed of the motor based on motor speed ripplegenerated by movement of residual water remaining in the drain pipeduring the rotating of the motor.
 14. The laundry treatment machineaccording to claim 13, wherein the controller is configured to controlthe speed of the motor to decrease sequentially or to decrease stepwiseas the motor speed ripple increases.
 15. The laundry treatment machineaccording to claim 13, further comprising an output current detector todetect an output current flowing to the motor, wherein the controller isconfigured to calculate a lift based on the output current, wherein thelift corresponds to a difference between a water level of a waterintroduction part flowing into the drain pump and a water level of awater discharge part discharged from the drain pump.
 16. The laundrytreatment machine according to claim 15, wherein the controller isconfigured to change a rotational speed of the motor based on thecalculated lift.
 17. The laundry treatment machine according to claim17, wherein the controller is configured to rotate the motor at a firstspeed, wherein, when the speed of the motor, determined based on theoutput current, is a second speed during the rotation of the motor atthe first speed, the controller is configured to calculate the lift as afirst level based on the second speed.
 18. The laundry treatment machineaccording to claim 17, wherein the controller is configured to change arotational speed of the motor based on the calculate lift such that thespeed of the motor is to decrease while the water level of the waterintroduction part is to be lowered.